A few notes about how I got working fprint in Ubuntu Karmic (since all available HOWTOs treat old versions, other distros or other fingerprint frameworks).

  - Install package libpam-fprint
  - Run the script "pam_fprint_enroll" and follow instructions
  - edit the file /etc/pam.d/common-auth, adding the line

    auth    sufficient                      pam_fprint.so

    ***before** the line

    # here are the per-package modules (the "Primary" block)

That's it: when you reboot, you should be asked to authenticate via the fingerprint reader (and only if it fails via password).

Notice that:
  - Unfortunately, fingerprint authentication after suspends/screen lock doesn't work (I don't even know if it would with a more advanced configuration).
  - Unfortunately - but that's not a missing feature, it's just that it couldn't be different - if your password for the account is also used to unlock the gnome keyring, you will have to enter it (when you login with the fingerprint)

So I personally think that fprint is at the moment quite useless. An exception may be its usage for sudo/gksudo/policykit authentication.